A group III nitride semiconductor attracts attention as a material for a next generation low power consumption illumination or a radio frequency and high power electronic device. The group III nitride semiconductor is applied to ultraviolet, blue, green, and white light emitting diodes or ultraviolet, blue, and green laser diodes, or a radio frequency and high power electronic device. Specifically, for the illumination purpose studies on a method of manufacturing a high power light emitting diode as an alternative to a fluorescent lamp are being actively conducted.
When the group III nitride semiconductor is grown on a underlying substrate, in many cases, an upper surface of the underlying substrate becomes a plane of a {000} plane group. The characteristics of the group III nitride semiconductor which is grown on the plane of the {0001} plane group tend to be degraded due to spontaneous polarization effect between a group III atom and a group V atom or a piezo electric field effect caused by the big difference between an interatomic distance of the group III atom and an interatomic distance of the group V atom. In other words, when the group III nitride semiconductor is used for a light emitting element such as the light emitting diode or the laser diode, carriers in a quantum well are spatially separated and light emitting recoupling of the carriers in an active layer is hindered, which lowers efficiency in the light emitting element.
To address the problem, it has been suggested to use a plane of a no-polarity (non-polar) {1-100} plane group or a plane of a {−12-10} plane group or a plane of a small polarity (semi-polar) {10-12} plane group as an upper surface of the underlying substrate. Among them, a group III nitride semiconductor obtained by growing a plane of the {1-100} plane group on the underlying substrate as the upper surface of the underlying substrate has a good doping or composition control characteristic, which may especially receive attention.
Patent Literature 1 discloses that a GaN based nitride semiconductor is crystal-grown on a sapphire substrate which has a (1-100) plane (m-plane) as a main plane. Even though the main plane of the sapphire substrate is ideally a just m-plane, the main plane may be most preferably a crystal surface which is tilted at ±0.5° or less in both a-axis direction and c-axis direction from the just m-plane as acceptable error range. By doing this, according to Patent Literature 1, it is possible to obtain a good quality epitaxial growth film of a GaN based nitride semiconductor.